Removeable closures for fiber/resin casing ends conventionally comprise a head which fits closely in the casing and is held in place by a segmented retaining plate or a snap ring inserted in an annular groove machined in the inner surface of the casing. When the closed casing is internally pressurized, the pressure force transmitted from the head to the casing (through the retaining plate or ring) is countered by the resistance of the casing end to delamination. As a result of cutting the annular groove, the fiber portions between it and the casing end no longer extend into the casing wall and delamination is resisted only by the shear strength of the resin between the outermost of the latter, short fiber portions and the composite structure surrounding them. That is, for failure to occur, it is only necessary to push out the (cylindrical) portion of the casing end comprising the severed fiber ends. No benefit is realized in this regard from the inherent tensile (and shear) strength of the fibers themselves. Such failure can be prevented by abutting the casing end against a suitably supported cage--or cradle--end but the advantages of composite materials as to light weight and space utilization will thereby be substantially negated.
The foregoing problem is largely avoided by a prior design (of the present inventor) illustrated in FIG. 3 of the drawings. This design has not previously been disclosed but was embodied in a commercially utilized utrafiltration device. In the latter design, the groove for the retaining plate is formed, not by cutting, but by bowing the (resin-coated) fibers over an annular bulge in the preform on which they are wound. The spaces next to the bulge, between the bowed fiber portions and the pre-form, are filled (after the form is removed) with an epoxy (or other) resin. A segmented retaining ring is employed.
The latter design vectors the forces so they are resisted by the shear strength of the fibers themselves and is highly satisfactory for many applications. However, it is considered not to provide adequate strength for relatively large diameter casings to be subjected to internal pressures of the magnitude commonly required for reverse osmotic desalination of saline waters.